1. Field of the Invention
This invention relates to the field of aviation. More specifically, the invention comprises a flight instrument which clearly displays the attitude and motion of a hovering aircraft to its pilot.
2. Description of the Related Art
The present invention primarily applies to aircraft which are in low-speed or hovering flight. It is useful in conventional rotorwing aircraft such as helicopters and “unconventional” hovering aircraft such as the Bell/Boeing V-22 Osprey and the McDonald Douglass AV-8B Harrier II.
Although the flight dynamics of a hovering aircraft will be familiar to those skilled in the art, a brief explanation of these dynamics may be helpful. Because a helicopter is the most common type of hovering aircraft, it will be used as an example. FIG. 1 shows a prior art helicopter 10, having main rotor 12 and tail rotor 14. FIG. 2 shows a “ghosted” view of the same helicopter with the conventional six degrees of freedom being shown with reference to its center of gravity 16. These six degrees of freedom are: (1) vertical translation 28 along yaw axis 22; (2) forward/rearward translation 26 along roll axis 20; (3) lateral translation 24 along pitch axis 18; (4) roll about roll axis 20; (5) pitch about pitch axis 18; and (6) yaw about yaw axis 22. Other degrees of freedom are typically present, but are not as significant as the six degrees just listed. In order to achieve control in hovering flight, a pilot must control these six significant degrees of freedom.
Those skilled in the art will know that a helicopter pilot controls the aircraft while in a hovering state by: (1) adjusting the collective pitch main rotor control; (2) adjusting the cyclic pitch main rotor control; and (3) adjusting the pitch of the tail rotor (primarily to control yaw). The pilot typically observes objects outside the helicopter to discern the helicopter's motion and then provide appropriate control input. Flight instruments are also available, such as an attitude indicator. An attitude indicator does provide information about the aircraft's roll and pitch states. A separate directional gyro can provide information about the aircraft's yaw state. It is also true that an airspeed indicator provides forward speed and a vertical speed indicator provides information regarding upward and downward motion, but these instruments do not provide an integrated and readily perceived picture of the aircraft's motion, especially the slower motion occurring while hovering.
A controlled hover requires that all three of the aforementioned controls be continually adjusted (as well as the throttle in some circumstances). Hovering is a very difficult task to learn. A student simply does not have time to scan and mentally integrate the currently available flight instruments and—even if a student did have enough time—the current instruments provide only partial information about the aircraft's motion. The result is that many students who are capable of learning to fly a helicopter in the aerodynamic flight regime (flight above approximately 30 mph) fail to master the art of hovering and maneuvering at low speeds.
Computer simulations are now used extensively in flight training, and this has been true for hovering aircraft as well. There was an initial belief that computer simulations could aid the teaching of hovering skills. When this initially proved unsuccessful, the suspected problem was a lack of visual resolution in the simulation. However, as more and more detailed simulations evolved, the problem persisted. It was eventually realized that the problem did not lie in the simulation's ability to mimic the real world, but rather with the fact that the information available to a hovering pilot in the real world is ambiguous. FIGS. 3-6 illustrate this phenomenon.
FIG. 3 shows a pilot's view looking out the front of the helicopter's canopy. The helicopter is hovering over the centerline of a runway having a heading of 270 degrees (“Runway 27”). The pilot can observe many features in the terrain surrounding the helicopter. Examples are runway 36, runway centerline 38, and runway numeral 40. The pilot can perceive the helicopter's motion by observing how these external objects move with respect to the helicopter. Even small motions can be discerned by observing how the external objects appear in relation to fixed portions of the helicopter—such as vertical canopy brace 34, horizontal canopy brace 32, and instrument console 30.
The reader will gain some understanding of these observations by comparing FIG. 4 to FIG. 3. FIG. 4 represents the pilot's view at a slightly later time than FIG. 3. The reader will observe that the runway appears to be “slipping under the nose” of the helicopter. In FIG. 4, runway numeral 40 has been partially occluded by horizontal canopy brace 32. Making this observation is easy. However, understanding what the observation means in terms of the motion of the helicopter is much more difficult.
Observing that objects in front of the helicopter appear to be “slipping under the nose” can mean three different things. These are shown in FIGS. 4A-4C. The helicopter can be: (A) ascending; (B) moving forward; and/or (C) pitching upward. Of course, in many instances, the motion will actually be a combination of these phenomena. Referring to the aircraft state diagram shown in FIG. 2, ascending would be vertical translation 28, moving forward would be forward translation 26, and pitching upward would be pitching about pitch axis 18.
The same problem exists when looking at objects out the side of the helicopter. FIG. 5 shows the pilot's view out side window 42. The pilot can observe many external objects, such as runway 36, taxiway 46, runway boundary 48, and runway threshold markers 44. The motion of these external objects can be observed with respect to the frame of the window and side canopy brace 50. FIG. 6 shows the same view a short time later. The reader will observe that the external objects appear to be slipping beneath the right side of the helicopter. However, as for the case of looking out the nose of the helicopter, these lateral visual cues are ambiguous.
Observing that objects to the right of the helicopter appear to be “slipping under the side” can mean three different things. FIG. 7 illustrates these possibilities. The helicopter can be: (A) ascending; (B) translating to the right; and/or (C) rolling to the left. Again returning to FIG. 2, the possible motions correspond to vertical translation 28, lateral translation 24, and/or rolling about roll axis 20. The motion will again likely be a combination of two or more of the possibilities. Resolving the ambiguity is an exceedingly complex task.
Similar visual ambiguities occur when making observations out the left side of the helicopter, and when trying to discern rearward motion. An experienced pilot is able to resolve these ambiguities, though the present view is that different pilots likely use different techniques to do so. There is no clearly defined method for teaching these skills. Instead, an instructor pilot (“IP”) usually gives the student control of only one input parameter while the IP controls the rest. As an example, the IP often controls the throttle, the collective pitch control, and the rudder pedals. The student would then be given command of the cyclic pitch control. The student hopefully masters the skill of hovering for each of the controls. More and more control authority is given to the student until he or she is able to control all the input parameters while performing hover maneuvers. Of course, some student pilots are ultimately unable to master this skill.
Those skilled in the art will know that helicopters and other hover-capable aircraft include a battery of flight instruments. A typical instrument cluster would include an attitude indicator, an airspeed indicator, a vertical speed indicator, a gyro compass, and a turn/slip indicator. These instruments are certainly useful, but they do not resolve the motion ambiguities present during hover maneuvers. The pilot must also continually scan the instruments in order to mentally integrate the information they are displaying. In a hover maneuver, there is rarely enough time to perform such a scan and mental integration.
In addition, even if the scan and mental integration step could be performed rapidly enough, existing flight instruments simply do not provide enough information for hovering maneuvers. As one example, they provide no indication of lateral translation. It is therefore desirable to provide a flight instrument which provides clear information about the motion and attitude of the aircraft during hovering maneuvers. The present invention provides such a flight instrument.